The present invention relates to a thread wound golf ball. More particularly, it relates to a thread wound golf ball having long flight distance, while maintaining the characteristics peculiar to the conventional thread wound golf ball, i.e. good shot feel and excellent spin performance.
Many golf balls are commercially selling, but they are typically classified into solid golf balls such as two-piece golf ball, three-piece golf ball and the like, and thread wound golf balls. The solid golf ball consists of a solid core of molded rubber material and a cover of thermoplastic resin (e.g. ionomer resin) covering on the solid core. The thread wound golf ball consists of a solid or liquid center, a thread wound layer formed on the center and a cover of ionomer resin or balata etc. having a thickness of 1 to 2 mm covering on the thread wound layer.
The thread wound golf ball, when compared with the solid golf ball such as two-piece golf ball, has better shot feel at the time of hitting and better controllability at approach shot. The thread wound golf ball is generally approved of or employed by high level golfers, especially professional golfers, who regard the characteristics as most important. However, the thread wound golf ball is inferior in flight distance to the solid golf ball, because the thread wound golf ball has large spin amount and small launch angle.
In the thread wound golf balls, there are two types, such as one having a solid center formed from integrally molded rubber material and the other having a liquid center composed of a hollow rubber sphere and liquid encapsulated in the sphere. Among them, a thread wound golf ball with a liquid center and a balata (trans-polyisoprene) cover is particularly approved of or employed by high level golfers, especially professional golfers, because of good shot feel and excellent controllability at approach shot. The thread wound golf ball with a solid center, when compared with the thread wound golf ball comprising a liquid center, has excellent flight distance, because the rebound characteristics of the center also have an effect on the rebound characteristics of the golf ball itself. However, the thread wound golf ball is generally inferior in flight distance to the solid golf ball as described above, and it is required to improve the flight distance, while maintaining the characteristics peculiar to the thread wound golf ball.
In order to solve the problem, a thread wound golf ball with a solid center, which has further excellent shot feel and controllability and long flight distance mainly by adjusting physical properties of the solid center, such as a diameter, hardness and hardness distribution; and physical properties of the cover, such as a hardness and flexural modulus to suitable ranges, has been proposed in Japanese Patent Kokai Publication Nos. 271537/1997, 201881/1998 and 51400/2000, Japanese Patent No. 2751022 and the like. A thread wound golf ball with a solid center, of which dimple properties has been considered as the other factor with respect to the flight performance in addition to the physical properties of the solid center and cover, has been also proposed in Japanese Patent No. 2886804.
However, the thread wound golf ball, which has sufficient flight distance as same as solid golf balls, while maintaining the advantage of good shot feel and excellent controllability in the thread wound golf balls, has not been obtained. Therefore the thread wound golf ball having further excellent shot feel and controllability and long flight distance is required.
A main object of the present invention is to provide a thread wound golf ball, of which the flight distance is improved, while maintaining good shot feel and excellent spin performance.
According to the present invention, the object described above has been accomplished by adjusting a diameter and deformation amount of the solid center, and a hardness of the cover to a specified range, thereby providing a thread wound golf ball, of which an initial flight performance such as a launch angle and spin amount is optimized, while maintaining good shot feel and spin performance; and by adjusting a dimple volume ratio to a specific range in connection with the cover hardness, that is, by optimizing a trajectory in connection with the initial flight performance, thereby providing a thread wound golf ball, of which the flight distance is improved as long as possible, in a thread wound golf ball comprising a solid center.